High (secondary) explosives with extremely high thermal stability are useful in both civilian and military applications. The major civilian use of such materials is in shape charges for increasing the yield of oil wells by penetrating the surrounding rock. Shaped charges are used for the purpose, among others, of making hydraulic communication passages, called perforations, in wellbores drilled through earth formations so that predetermined zones of the earth formations can be hydraulically connected to the wellbore. Perforations are needed because wellbores are typically completed by coaxially inserting a pipe or casing into the wellbore, and the casing is retained in the wellbore by pumping cement into the annular space between the wellbore and the casing. The cemented casing is provided in the wellbore for the specific purpose of hydraulically isolating from each other the various earth formations penetrated by the wellbore.
The (secondary) explosive in “down hole penetrators” must often withstand temperatures greater than about 200° C. for several hours up to a day or more and still initiate and perform reliably. In addition, as with all applications involving explosives, the performance needs a maximum output with a minimum of sensitivity. Currently, one explosive of choice for down hole penetrators used at high temperatures is 2,2′,4,4′,6,6′-hexanitrostilbene (HNS), see, e.g., U.S. Pat. No. 4,527,481. HNS has the advantage of having a high thermal stability (315° C.) with a reasonably good performance. Disadvantages of HNS include its relative sensitivity and a high cost due to a lengthy purification process. Another potential explosive for down hole penetrators is DAAF (diaminoazoxyfurazan). DAAF has an 18% better penetration performance than HNS and it is more insensitive to mechanical stresses while still remaining initiable. A disadvantage of DAAF is it has thermal stability to only 250° C. which is too low for some oil wells.
U.S. Pat. No. 3,166,567 describes compounds such as tetranitro-2,3:4,5-dibenzo-1,3a,6,6a-tetraazapentalene as insensitive explosive materials. However, that material is difficult to prepare due to low yields, the need for high temperatures for long periods and difficult purification and separation steps.
Recently, another compound, 2,4,8,10-tetranitro-5H-pyrido[3′,2′:4,5][1,2,3]triazolo[1,2-a]benzotriazol-6-ium, inner salt, was examined for potential application as a down hole penetrator. The synthesis of 2,4,8,10-tetranitro-5H-pyrido[3′,2′:4,5][1,2,3]triazolo[1,2-a]benzotriazol-6-ium, inner salt had been previously reported in the literature by Belgian scientists in 1983. In addition to the preparation of 2,4,8,10-tetranitro-5H-pyrido[3′,2′:4,5][1,2,3]triazolo[1,2-a]benzotriazol-6-ium, inner salt, the reference (Maquestiau et al., Bull. Soc. Chim. Belg., v. 92, no. 1, pp. 67-75,1983) reported a melting point of greater than 300° C. for the compound. When the compound was prepared in accordance with the description in the reference, the resultant compound was found to include residual acid when pressing the compound in metal dies resulted in etching of the metal dies. As use in a down hole penetrator typically involves use of a metal casing, such residual acid would be detrimental.
Accordingly, the development of an acid-free compound and a process of preparing such an acid-free compound was sought.